The present invention relates to a dispensing pump with improved sealing for application to liquid containers, and more particularly a pump able to prevent liquid seepage between the pump stem and the flange, even if the stem is displaced a short distance away from its rest position.
Manually operated pumps are known for mounting on liquid containers, to dispense quantities of the liquid each time the pump is operated. These pumps have a hollow stem which projects outwards from the pump by passing through a hole provided in a flange forming part of the pump. To prevent a vacuum forming within the container when liquid is dispensed therefrom, a passageway has to be provided to enable atmospheric air to penetrate into the container, in order to maintain the pressure within it substantially constant. Normally the passage of air takes place between the outer surface of the hollow stem and the opposing surface of the hole in the flange through which the stem passes and translates with reciprocating to-and-fro movement.
During pump operation there is no liquid seepage between the stem and the flange because the container and the pump mounted on it are held in a substantially vertical position, with the pump positioned at the top. When at rest, the container and the pump mounted on it lie in a horizontal or even downwardly inclined position, especially during storage and transport. To prevent the liquid contained in the container from seeping (leaking) between the outer surface of the stem and the opposing surface of the flange forming part of the pump, it is known to provide a profiled seat on the flange (about its hole through which the stem passes) and to cause to project from the stem a profiled annular element which (when the pump is at rest) is maintained urged by the pump spring against said profiled seat on the flange, so that it seals against it.
Pumps of the aforesaid type are well known and are described, for example, in U.S. Pat. No. 5,772,078, U.S. Pat. No. 4,960,230 (and in the equivalent EP-B0301615), and U.S. Pat. No. 6,286,726 (and in the equivalent EP-B-1033174).
These pumps suffer from the drawback that, after they have been fitted (by the user) onto the container containing the liquid to be dispensed, if the container during its handling or transport is disposed horizontally or downwardly inclined, liquid can leak between the stem and flange of the pump, even if the pump stem has been displaced only a few tenths of a millimeter from its rest position as a result of an accidental stress transmitted to the stem from the outside.
The main object of the present invention is therefore to provide a pump able to prevent liquid leakage between the stem and flange of the pump, even if the stem is displaced from its closed rest position.
Another object is to provide a pump of the stated type, the structure and cost of which are substantially equal to those of a similar traditional pump.
These and further objects are attained by a pump comprising a cup-shaped body housing a translatable piston connected to a hollow stem, one end of which projects from the cup-shaped body via the hole in a flange mounted on the cup-shaped body, from the stem there projecting a profiled annular part which when the pump is at rest sealedly engages a profiled seat provided on the flange about its said hole, characterised in that from the flange there projects all about its said seat a hollow skirt the inner surface of which is cylindrical and against which there sealedly abuts the annular part projecting from the stem.
Preferably, the outer peripheral surface of the annular part of the stem presents at least one annular projection which engages the inner cylindrical surface of said skirt, the lower free surface of the annular part of the stem and/or the peripheral surface of the annular part of the stem being substantially conical, to facilitate the insertion of said annular part into the skirt.
It has been found that, for normal uses, said cylindrical skirt has a length such that the annular part of the stem remains in contact with and seals against it for a length up to 5 mm of the travel of the stem away from its rest position, however in the most common cases the length of said skirt can be such that said annular part remains in contact with and seals against it for a length less than 2.5 mm of the travel of the stem away from its rest position.